Abstract
On incubation with subtilisin, the raw starch-adsorbable and raw starch-digestive glucoamylase I (MW 90, 000) of Aspergillus awamori var. kawachi was converted to raw starch-inadsorbable and raw starch-indigestive glucoamylase I' (MW 83, 000), with the liberation of glycopeptide I (MW 7, 000). This inactive peptide showed significant adsorbability onto raw starch, fungal cell wall and chitin but not onto chitosan. It consisted of 42.1 % carbohydrate residues and amino acid residues, such as Asp5, Thr8, Ser4, Glu3, Gly4, Ala4, Val3 and His2, characteristically abundant in hydroxy amino acid. The adsorbability of glucoamylase I and glycopeptide I was supposed to take place through hydrogen bonds between the insoluble raw starch and the hydroxy amino acid situated at the position of glycopeptide I. The specific blocking of the amino acid residue suggested that the seryl residue on glycopeptide I played a role in the raw starch-affinity site on glucoamylase I that is essential for the digestion of raw starch.
